It has long been known that noise and exhaust emissions can be reduced at various engine operating conditions by fuel injection rate shaping. This process tailors the rate at which fuel is injected during the fuel injection cycle. One method of rate shaping that has proven effective at controlling emissions at idle engine operating conditions involves the utilization of a spill control device to create a split injection.
One example using a spill control device to create a split injection is presented in U.S. Pat. No. 5,492,098 to Hafner et al. Hafner uses a spill control device to briefly lower the pressure surrounding the needle valve member during the injection event to create a split injection at idle operating conditions. In Hafner, when the plunger is moving toward its advanced position, an annulus defined by the plunger opens the fuel pressurization chamber to a spill port, which is connected to a low pressure fuel return area. This causes a drop in pressure within the fuel pressurization chamber to below valve closing pressure, which in turn creates a dramatic drop in pressure in the nozzle chamber, thus allowing the biasing spring to act against the needle valve member to briefly close the nozzle outlet. Once the annulus has passed the spill port, the fluid connection between the fuel pressurization chamber and the low pressure area is closed. This causes the pressure in the nozzle chamber to increase and the needle valve member can again act against the action of the biasing spring to open the nozzle outlet.
The Hafner method creates a short time in between the split injections, referred to as dwell time. This dwell time is a function of various geometric features including the width of the annulus and the shape of the spill port, among others. While the Hafner injector has worked well to decrease undesirable emissions at idle engine operating conditions, the maximum dwell time capability for the Hafner injector is inherently limited by the stroke of its plunger. For instance, an annulus with a larger width would increase the dwell time, but may undermine performance at a rated operating condition. For some applications there is a desire to increase the dwell time beyond the geometric constraints inherent in the Hafner fuel injector.
The present invention is directed to improving upon fuel spillage split injection devices by providing a broader range of possible dwell times.